The present invention relates to a magnetic gear for torque transmission in noncontact.
In recent years, flux modulated type magnetic gears, in which a rare earth magnet is made use of to materialize a high torque density, have been researched and developed (K. Atallah and D. Howe: A Novel High-Performance Magnetic Gear: IEEE Transactions on Magnetics, Vol. 37, No. 4, pp. 2844-2846). In addition, WO2009/087408 discloses an improvement in strength for constituent members of the magnetic gear, in particular, pole pieces.
Also, that construction, in which permanent magnets in a magnetic gear mechanism are divided in a thickness-wise stacking direction, is disclosed in “Consideration with respect to an Improvement in Strength for Permanent Magnet Type Magnetic Gears” (Journal of the Magnetics Society of Japan Vol. 33, No. 2, 2009). That construction, in which a rotor structure in a magnetic gear mechanism is made an interior permanent magnet type, is disclosed in “Consideration with respect to a Rotor Structure of a Permanent Magnet Type Magnetic Gear” (Journal of the Magnetics Society of Japan Vol. 34, No. 3, 2010).
The above-mentioned document “K. Atallah and D. Howe: A Novel High-Performance Magnetic Gear: IEEE Transactions on Magnetics, Vol. 37, No. 4, pp. 2844-2846” presents the principle and magnetic characteristics of a magnetic gear but does not analyze the mechanism and strength thereof.
On the other hand, WO2009/087408 discloses a method, in which one ends of pole pieces of a magnetic gear are joined to an end holding member to provide a rigid structure, thereby achieving an improvement in strength of the pole pieces. Since the pole pieces are formed from a laminated steel sheet, a soft magnetic composite, or the like, however, they are weak in strength and insufficient to achieve high torque driving and large sizing. Also, when a magnetic body is used for the end holding member, magnetic flux of a magnetic gear leaks toward the end holding member to cause decrease in torque transfer characteristics.
Further, WO2009/087408 also discloses a method, in which metallic bars separate from pole pieces are used, both ends of the bars, respectively, are joined to first and second metallic end holding members, and the pole pieces are electrically insulated from the metallic bars to be molded, thereby achieving improvement in strength. However, current loop is formed by the connection of the metallic bars and the metallic end holding members, an induced-current is generated on the metallic bars and the metallic end holding members at the time of driving, and, in particular, a sharp increase in loss is caused at the time of high-speed driving. Also, in the case where the metallic end holding members are formed from a magnetic body, magnetic flux of a permanent magnet leaks toward the end holding members to cause decrease in torque transfer characteristics. In addition, loss caused by an eddy current through a magnetic gear is analyzed in “Consideration with respect to an Improvement in Strength for Permanent Magnet Type Magnetic Gears” (Journal of the Magnetics Society of Japan Vol. 33, No. 2, 2009) and “Consideration with respect to a Rotor Structure of a Permanent Magnet Type Magnetic Gear” (Journal of the Magnetics Society of Japan Vol. 34, No. 3, 2010), but the mechanism and strength of a magnetic gear is not analyzed therein.
The invention has been thought of in view of the above-mentioned problems and has its object to provide a magnetic gear, in which an improvement in strength is achieved for pole pieces and a decrease in loss is made possible.